1. Field of the Invention
The present invention relates to a broadband wireless communication system. More particularly, the present invention relates to an apparatus and method for frequency-selectively allocating a resource to a mobile station connected to a relay station in a broadband wireless communication system.
2. Description of the Related Art
In a next generation communication system, also known as the 4th Generation (4G) communication system, researches are actively in progress to provide a Quality of Service (QoS) with a data transfer speed of about 100 Mbps. More particularly, in a Broadband Wireless Access (BWA) system, such as a wireless Local Area Network (LAN) system and a wireless Metropolitan Area Network (MAN) system, there is research on a communication system that supports a high speed service at the same time as providing mobility and ensuring QoS. An example of such a communication system is an Institute of Electrical and Electronics Engineers (IEEE) 802.16 communication system, which standard is hereby incorporated by reference.
The IEEE 802.16 communication system employs an Orthogonal Frequency Division Multiplexing (OFDM)/Orthogonal Frequency Division Multiple Access (OFDMA) scheme so as to allow a physical channel of the wireless MAN system to support a broadband network.
FIG. 1 illustrates a frame format of a conventional IEEE 802.16 communication system.
Referring to FIG. 1, a frame roughly includes a downlink frame 110 and an uplink frame 120.
The downlink frame 110 includes a preamble 111, a MAP 113 and a downlink data burst 115. The preamble 111 is a signal for synchronizing the frame during communication, and is also used to estimate a channel between a Base Station (BS) and a Mobile Station (MS). The MAP 113 is a signal for broadcasting resource allocation information to a plurality of MSs. The downlink data burst 115 is a signal for data transmitted from the BS to the MS.
The uplink frame 120 includes uplink control information 121 and an uplink data burst 123. The uplink control information 121 is a signal for data in association with resource allocation request, channel quality and so on. The uplink data burst 123 is a signal for data transmitted from the MS to the BS.
In the IEEE 802.16 communication system which uses the aforementioned frame format, an MS estimates a channel by using the preamble 111 received from a BS, and the BS receives information on the channel from the MS by using the uplink control information 121. Accordingly, the BS determines a preferable frequency band by using the channel information, and thus determines a suitable modulation and encoding method.
In order to ensure mobility of the MS and flexibility of implementing a wireless network in the IEEE 802.16 communication system, researches on the further effective provision of services are actively conducted in a wireless environment where traffic distribution and call demands rapidly change. For example, a communication system is taken into account to cope with these demands, in which one fixed (or mobile) Relay Station (RS) or general mobile phones are used to transfer data based on a multi-hop relay scheme.
In the broadband wireless communication system, the RS is used to increase coverage or improve throughput. When the RS is used to increase coverage, the RS receives and relays all signals transmitted from the BS and the MS. On the other hand, when the RS is used to improve throughput, the RS does not relay a control signal (e.g., preamble, MAP message, etc.) and instead relays only user data other than the control signal. That is, the BS and the MS transmit/receive the control signal such as the preamble 111 through a direct link channel and transmit/receive the downlink data burst 115 and the uplink data burst 123 via the RS.
As such, when the RS is used to improve throughput and thus dose not relay the control signal, the MS transmits/receives the control signal through a link between the MS and the BS and transmits/receives data signal through a link between the MS and the RS. The estimated channel information between the MS and the BS is different from information on a channel for transmitting the data signal between the MS and the RS. Therefore, when the RS does not relay the control signal, there is a problem in that a preferable frequency band for a data signal and a suitable modulation/encoding method cannot be determined.